1. Field of the Invention
The present invention generally relates to a method of and a device for molding and shaping fiber reinforced resinous material and, more particularly, to a method of and a device for molding and shaping a semi-cured molding material (either sheet molding compound or thick molding compound) comprising unsaturated polyester resin or epoxy resin mixed with a high temperature curing agent and reinforcement fibers such as, for example, glass fibers impregnated with the resin to provide a shaped article of manufacture of any desired shape wherein the reinforcement fibers are oriented in any desired direction.
2. Description of the Prior Art
Conventionally, there are two methods for molding a compound consisting of reinforcement fibers such as glass fibers or carbon fibers, resin, and a curing agent into a required configuration. According to one of those methods, the reinforcement fibers, resin, and the curing agent are mixed with each other during the molding operation. That is, a wet material is used in this method. According to the other method, a prepreg sheet, for example, a fiber reinforced resin such as a sheet molding compound (SMC) or a thick molding compound (TMC) consisting of the above described semi-cured reinforcement fibers, resin and the curing agent is used to mold the material by use of a press. That is, a dry material is used in this method.
The conventional molding method utilizing the dry material such as the sheet molding compound is superior and widely used because it does not cause environmental pollution unlike the method using the wet material; the sheet molding compound can be treated easily during the molding operation; and the surface of the resultant product is glossy. The material can be molded into products having complicated shapes with highly accurate dimensions.
The dry molding of the compound such as the fiber reinforced resinous material is carried with a thermal compressive molding method in which a press and a mold are generally utilized. By way of example, after the compound cut to a predetermined shape covering an inner mold surface has been inserted into the lower mold, an upper mold is pressed under a high pressure against the lower mold so that, within the cavity defined between the upper and lower molds, the compound can be shaped. At the same time, this press molding is carried out at a high temperature and, during this press molding, a compound is also cured simultaneously.
However, according to the conventional press molding method, the high pressure of 1.2 MPa is applied to the composite material all at one time. Therefore, the composite material fluidizes abruptly with the consequence that the reinforcement fibers in the composite material are biased in an unexpected direction, making it impossible to control the orientation of the reinforcement fibers.
In the composite material generally used in the practice of the press molding method, the reinforcement fibers contained therein are not oriented in a particular direction and are substantially uniformly oriented in all direction. Therefore, the composite material is prepared having an isotropy in which the strength relative to any direction is uniform. However, as hereinbefore discussed, there is a problem in that during the press molding, the reinforcement fibers are oriented in an unexpected direction. Accordingly, for example, where the molded article is required to have an isotropic strength, the strength may vary depending on the direction making it impossible for the resultant article to satisfy the requirements. On the other hand, where the molded article is required to have a so-called anisotropic strength in which the strength in one particular direction is higher than that in any other direction, it is difficult to control the reinforcement fibers to be oriented in the particular direction, thereby failing to satisfy the intended requirements.
Also, when the composite material is to be molded into a predetermined shape under the high pressure applied all at one time by the press, the flow of the material varies from one place to another within the molding cavity of the press. Therefore, an peeling, an laminar separation, and an interlayer undulation tend to occur and, at the same time, the raw material will not be uniformly distributed, resulting in a defect in the eventually shaped products. Where the fiber reinforced resinous material such as the sheet molding compound is to be press-molded, a limitation in the mold design makes it difficult to mold the article in a generally elongated configuration.
Thus, in order to mold the fiber reinforced resinous material continually, the method utilizing the wet material has been widely used wherein, after the continuous reinforcement fibers have been impregnated with a resinous material, the reinforcement fibers are pulled from the cavity of the die by the application of a relatively great pulling force.
However, where the articles are to be continuously manufactured using the wet material as described above, the application of the relatively great pulling force results in an increased power consumption. In addition, the expensive continuous reinforcement fibers results in an increased manufacturing cost. While the plural reinforcement fibers are pulled into a bundle, the reinforcement fibers tend to be randomly aligned and cause deterioration the physical properties of the molded parts. Furthermore, it is difficult to mold the article of relatively large size and complicated shape.